1. Field of the Invention
The present invention mainly relates to copper foil suitable for electromagnetic shielding of a display, more particularly relates to a copper foil used as a material for making an electromagnetic shield suitable for a plasma display panel (PDP), a method of production of the same, and an electromagnetic shield made by that copper foil.
2. Description of the Related Art
Optoelectronic components and other electronic equipment are becoming remarkably more sophisticated and advanced. In particular, optoelectronic image displays are rapidly spreading in use for television receivers, computer monitors, etc. In recent years, in particular, market demand has been rising for the new large flat screen displays. Recently, large flat screen PDPs have come into the spotlight.
PDPs, however, in principle emit strong electromagnetic waves. Electromagnetic waves are liable to interfere with various instruments and may have an effect on human health as well. Recently, legal regulations regarding emission of electromagnetic waves have therefore become tougher. For example, there are the U.S. Voluntary Control Council for Interference by Data Processing Equipment: Electronic Office Machines (VCCI) of the Federal Communication Commission (FCC), the Japanese Electrical Appliance and Material Control Law, and other product regulations.
An electromagnetic shield has to be conductive over the entire surface and be superior in transparency. To meet these requirements, in practice, a transparent conductive thin film is sometimes provided over the entire surface of a PDP as an electromagnetic shield. Such a PDP, however, ends up with reduced transmittance of the transparent conductive layer itself if trying to obtain an electromagnetic shielding ability of for example at least 60 dB.
To solve this problem, the method has been proposed of inserting fine metal wires woven into a mesh between films or glass or polymer substrates to form an electromagnetic shield. However, a weave of fine metal wires easily becomes twisted and if combined with a PDP, problems in appearance such as moire patterns occur.
Therefore, further, the method has been proposed of bonding metal foil, particularly copper foil, to a transparent polymer film using an adhesive, then forming a mesh pattern in the metal foil by etching. The metal parts, however, are substantially opaque, so raising the transmittance was a difficult problem.
On the other hand, in recent years, when processing metal foil into electromagnetic shields, shedding of particles from the metal foil and uneven color of the surface of the metal foil have come to be viewed as problems.
Research is also proceeding on the particle shedding from copper foil and the electroforming solutions eliminating toxic substances. Copper foil for printed circuit boards was previously disclosed by the assignee in Japanese Unexamined Patent Publication (Kokai) No. 11-256389. With the technology disclosed in Japanese Unexamined Patent Publication (Kokai) No. 11-256389, however, the hue or evenness of color required for an electromagnetic shield and measures against particle shedding cannot be said to be sufficient.